The invention relates to an assembly for adjusting mobile elements of furniture, with a motor displaying a first and a second connection, a control circuit for controlling the motor, which is provided with at least a first push-button switch for controlling the motor, a power supply circuit with an operating voltage output, with a mains connection located between a mains plug that can be connected to an alternating-current mains and the power supply circuit, with a relay displaying a relay switch and a control input controlling the relay switch, where the relay switch is located in the mains connection and is in OFF position when unexcited, and with an auxiliary power source that can be connected to the control input of the relay.
An assembly of the kind mentioned above is known from European Patent Specification 0 615 667 B1. The assembly described therein for safety isolation of control devices from the mains refers to an assembly for adjusting mobile elements of furniture that is provided with two motors. One motor displays a first and a second connection. Furthermore, a control circuit comprising a first and a second push-button switch is provided for each motor. The control circuit of a motor also includes a first and a second relay. The relay coil of the first relay is connected to operating potential via the first push-button switch and the relay coil of the second relay via the second push-button switch. The relay switches of both relays are designed as changeover switches, where one changeover contact is connected to the operating voltage output of the one polarity and the other changeover contact with the operating voltage output of the other polarity. The centre contact of the relay switch of the first relay is connected to the first connection of the motor and the centre contact of the relay switch of the second relay to the second connection of the motor. In unexcited state, the relay switches each establish a connection between their centre contact and the operating voltage output with the same polarity as on the respective other relay switch.
In this known assembly, the operating voltage source is designed as a direct-current source and each motor as a direct-current motor. As a result, the design of the control circuit provides control of the direction of the motors. If, for example, the first push-button switch is operated, the first relay picks up and switches over the relay switch. While the first and second connection of the motor had the same potential up to that time, the switching operation now connects the first connection to the other operating voltage potential. The motor thereupon performs motion in one direction until the first push-button switch is released. If the second push-button switch is subsequently operated, the second relay picks up, thereby reversing the polarity on the motor and causing the motor to move in the other direction.
In this known assembly, there is also a third relay with a relay switch located in the mains lead to the power supply circuit. An auxiliary power source is connected in parallel to the operating voltage output of the power supply circuit. This auxiliary power source is connected to the control input of the third relay via each of the push-button switches.
Since the relay switch of the third relay is in OFF position when unexcited, the power supply circuit is initially isolated from the mains. If one of the push-button switches is now operated, the voltage of the auxiliary power source is applied to the control input of the third relay via the push-button. This relay picks up as a result and switches its relay switch to the ON position. The power supply circuit is thereby connected to the mains voltage and supplies an operating voltage at its operating-voltage output. As a result, each of the relays forming part of the control circuit can pick up, provided the associated push-button switch is pressed. The motor thereupon performs its adjusting motion. The third relay remains operational during this time, since its control input is now supplied with operating voltage. If the push-button switch is released, for instance because the necessary adjusting motion has been completed, the relay associated with the respective push-button drops off, as does the third relay, and the circuit arrangement is once again isolated from the mains.
The disadvantage of this arrangement is that each push-button switch has to be provided with a relay, meaning that the circuit arrangement not only requires a considerable amount of space, but is also complex and expensive to manufacture.
Consequently, the object of the invention is to disclose an assembly for adjusting mobile elements of furniture that can be constructed more easily and cost-effectively while maintaining safety isolation from the mains, i.e. isolation from the mains during times when no control functions have to be executed and connection to the mains when control commands are received.
According to the invention, this object is solved in that the first push-button switch forms an electric circuit with the motor and the operating voltage output. Moreover, either the control input of the mains isolating relay is connected in parallel to the motor, or a rectifier bridge known as a Graetz bridge is connected between the motor and the control input of the mains isolating relay. A rectifier bridge of this kind is provided with four diodes, of which two first diodes have their cathodes interconnected in a positive node, while their anodes are each interconnected with the cathodes of the two second diodes in an alternating-current node. In this context, the first and second connections of the motor are each connected to an alternating-current node. The positive and negative nodes are each connected to the control input of the mains isolating relay.
The first alternative provides for the simplest realisation of the solution according to the invention, where both the motor and the mains isolating relay are connected directly by the first push-button. In this context, the relay switch of the mains isolating relay is in OFF position when in quiescent state. Consequently, the power supply circuit is not connected to the mains. If the first push-button is pressed in order to start the motor, the voltage from the auxiliary power source is applied via the first push-button switch to the mains isolating relay, which picks up and connects the power supply circuit to the mains. Operating voltage is then present at the operating-voltage output and the mains isolating relay is held in picked-up state by the operating voltage for as long as the first push-button switch is pressed. When it is released, the voltage at the control input of the mains isolating relay is interrupted and this mains isolating relay drops off. The power supply circuit is then no longer connected to the mains, since the relay switch of the mains isolating relay is once again in OFF position.
The second alternative of the solution according to the invention displays the same mode of operation. When the push-button switch is pressed, the voltage from the auxiliary power source is applied to the control input of the mains isolating relay via the rectifier bridge, causing the mains isolating relay to pick up and connect the power supply circuit to the mains for as long as the push-button switch is pressed. However, interconnection of the rectifier bridge avoids feedback from the control input of the mains isolating relay to the motor connections. This permits the use of several motors, for example, all of which operate with one mains isolating relay, as described in more detail below.
In one embodiment of the invention, provision is made for the operating-voltage output to be designed as a DC output and the motor as a DC motor.
Designing the invention with DC motors offers not only favourable torque distribution, but also the advantage of simple control of the sense of rotation of the motors.
Especially for simple control of the sense of rotation of the DC motors, a further embodiment of the invention provides for the inclusion of a second push-button switch and for both the first and the second push-button switch to be designed as changeover switches. One of their changeover contacts is connected to the operating-voltage output of the one polarity, while the other changeover contact is connected to the operating voltage of the other polarity. The centre contact of the first push-button switch is connected to the first connection of the motor, and the centre contact of the second push-button switch is connected to the second connection of the motor. When not operated, each push-button switch displays a connection between its centre contact and the operating-voltage output with the same polarity as the other push-button switch.
This arrangement makes it possible to cause the motor to rotate in one direction with the first push-button switch and in the other direction with the second push-button switch. In this context, either one push-button switch or the other must be operated in order to obtain rotation. Simultaneous operation would not, however, be dangerous. It would merely not cause any movement of the motor.
In another embodiment of the invention, there is provision for the motor assembly, comprising the motor and the first or the first and second push-button switch, to be present at least in duplicate. In this context, each motor assembly can be provided with a mains isolating relay, the control input of which is connected in parallel to the associated motor, while the relay switches of all mains isolating relays are connected in parallel to each other. Alternatively, each motor assembly can be provided with a rectifier bridge, the alternating-current node of which is connected to the connections of the respective motor and whose positive and negative nodes are each jointly connected to the control input of one and the same mains isolating relay.
This embodiment makes it possible to use several motors that can be controlled directly by one control circuit, meaning that an interconnected relay is avoided while preserving the possibility of safety isolation from the mains. When a motor is switched on, operating voltage is present between its first and second connections. If several motors were then connected to one and the same mains isolating relay, the connection of the mains isolating relay in parallel to the motors would cause the operating voltage to cross from the activated motor to the others. This is prevented either by the rectifier bridge connected between each motor and the one mains isolating relay, or by installing several, separate mains isolating relays.
In another embodiment of the invention, there is provision for the auxiliary power source to consist of an alternating-current source. In this context, it is conceivable for an auxiliary transformer to be provided, the secondary output of which is connected in parallel to the operating-voltage output of the power supply circuit. This provides an alternating voltage as the auxiliary power for switching on the mains isolating relay.
This kind of application of an auxiliary alternating voltage is conceivable both in an embodiment using AC voltage as the operating voltage and AC motors, and when using DC voltage as the operating voltage. In the latter case, either the AC voltage from the auxiliary power source could be rectified, or the auxiliary power source could display such a high internal resistance that DC components are not destroyed or switch off the auxiliary power source as soon as the mains isolating relay has picked up, for which purpose a separate relay switch can be provided, for example.
However, it must be noted that there is no complete safety isolation from the mains in this context, since the auxiliary power source remains connected to the mains as a power source in the circuit arrangement.
In a more favourable embodiment of the invention, the auxiliary power source consists of a direct-current source. In principle, it is possible for the direct-current source to again be designed with a mains connection, for instance using a transformer and a downstream rectifier circuit. Expediently, however, the direct-current source can also be designed as a direct-current source that is electrically isolated from the mains.
In one embodiment of the invention, this is realised in that the auxiliary power source consists of a capacitor. Capacitors with relatively low leakage currents are expediently used for this purpose in order to retain an existing charge for an acceptable period of time. As a general rule, assemblies according to the invention are operated at least once over a period of one week. This period will suffice to maintain the capacitor charge.
In the event that longer periods of non-use of the assembly according to the invention have to be bridged, operating reliability can be increased by providing a manual operating device on the relay contact of the mains isolating relay.
Another possibility for reliably maintaining the charge of the capacitor as the auxiliary power source is to provide a trigger circuit having a pulse output that is additionally connected to the mains isolating relay. This trigger circuit intermittently switches the mains isolating relay, as a result of which the power supply circuit briefly supplies operating voltage at its operating-voltage output, thus charging the capacitor back up to operating voltage potential. The interval between pulses is governed by the leakage current of the capacitor, making it possible also to use relatively inexpensive capacitors, which usually also have relatively high leakage currents. Even if a pulse interval of several minutes were to be selected, the influence of the alternating-current mains, which is essentially to be avoided by safety isolation from the mains, would be completely negligible.
Another embodiment of the auxiliary power source as a direct-current source consists in the auxiliary power source comprising a battery. Since batteries can have service lives of more than a year, especially if they are used only very rarely, as in the case in question, a battery ensures operational readiness at all times. Absent operational readiness in the event of a drained battery can be prevented by means of a regular maintenance cycle of the assembly according to the invention.
In a particularly favourable embodiment of the invention, provision is made for the mains isolating relay to display a second relay switch or, in the event of there being several mains isolating relays, for each mains isolating relay to display a second relay switch and for each of these relay switches to be located in a separate line of the mains connection.
This embodiment implements bipolar disconnection of the mains lead. This means that the downstream arrangement can be shielded not only from alternating electromagnetic fields, but also alternating electrical fields.